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Raju Nandhakumar,Yun Soo Ahn,Hoe-Jin Yoon,김관묵 대한화학회 2009 Bulletin of the Korean Chemical Society Vol.30 No.12
New receptors 1-3 that bind stereoselectively amino alcohols and convert chirality of amino acidsvia imine bond formation were synthesized. The receptors have uryl (1), thiouryl (2) and guanidinium (3) groups all with additional phenylcarbonyl motifs, which are effective hydrogen bonding donors and play a key role in the stereoselective recognitions. The stereoselectivities were measured from the integration of 1H NMR peaks. Compound 1 and 2 showed the stereoselectivities for the imine formation with amino alcohols (KR/KS) in the range of 2 ~ 4, and compound 3 in the range of 4 ~ 8. Chirality conversion efficienciesof 1-3 for amino acids, i.e. D/L ratio at equilibrium, are in the range of 1.5 ~ 5.6, showing a little higher efficiency with 3. The additional phenylcarbonyl motifs in 1-3 were revealed not to contribute to significant enhancement of the selectivities.
Nandhakumar, Raju,Ahn, Yun-Soo,Yoon, Hoe-Jin,Kim, Kwan-Mook Korean Chemical Society 2009 Bulletin of the Korean Chemical Society Vol.30 No.12
New receptors 1-3 that bind stereoselectively amino alcohols and convert chirality of amino acidsvia imine bond formation were synthesized. The receptors have uryl (1), thiouryl (2) and guanidinium (3) groups all with additional phenylcarbonyl motifs, which are effective hydrogen bonding donors and play a key role in the stereoselective recognitions. The stereoselectivities were measured from the integration of $^1HNMR$ peaks. Compound 1 and 2 showed the stereoselectivities for the imine formation with amino alcohols ($K_R/K_S$) in the range of 2${\sim}$4, and compound 3 in the range of 4${\sim}$8. Chirality conversion efficienciesof 1-3 for amino acids, i.e. D/L ratio at equilibrium, are in the range of 1.5${\sim}$5.6, showing a little higher efficiency with 3. The additional phenylcarbonyl motifs in 1-3 were revealed not to contribute to significant enhancement of the selectivities.
Hyein Jung,Raju Nandhakumar,Hoe-Jin Yoon,이상기,김관묵 대한화학회 2010 Bulletin of the Korean Chemical Society Vol.31 No.5
Novel H8-binaphthol-based chiral receptors appended with an uryl moiety (2a) and a guanidinium moiety (2b) have been designed and synthesized for the enantioselective recognition of 1,2-amino alcohols via reversible imine formation. The selectivities (KR/KS = 9.8 ~ 19.4) of 2b in imine formation with 1,2-amino alcohols are higher than those of 2a (KR/KS = 1.8 ~ 4.5). Similar efficiency trend have been observed in the conversion of L-amino acids to D-amino acids, i.e., the efficiency of the receptor 2b (D/L ratio: 4.3 ~ 10.1) is superior to 2a (D/L ratio: 4.0 ~ 8.7).
Lijun Tang,Raju Nandhakumar,Minghui Liu,Fangfang Li 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.9
A new rhodamine B-coumarin conjugate (1) capable of recognizing both Cu^2+ and Fe^3+ using two different detection modes have been designed and synthesized. The metal ion induced optical changes of 1 were investigated in CH_3CN-H_2O (1:1, v/v, HEPES 50 mM, pH = 7.0) solution. Sensor 1 exhibits selective colorimetric recognition of Cu^2+ and fluorescent recognition of Fe^3+ with UV-vis and fluorescence spectroscopy,respectively. Moreover, both of the Cu^2+ and Fe^3+ recognition processes are observed to be barely interfered by other coexisting metal ions.
Jiyoung Kim,Raju Nandhakumar,김관묵 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.4
Novel binol-based uryl and guanidinium receptors having higher ring conjugation at the periphery of the hydrogen bonding donor sites have been synthesized and utilized to study the enantioselective recognition of 1,2-aminoalcohols and chirality conversion of natural amino acids via imine bond formation. There is a remarkable decrease in the stereoselectivites as the conjugation increases at the periphery of hydrogen bonding donor sites. The guanidinium-based receptors show more selectivity towards the amino alcohol than that of the uryl based ones due to its charge reinforced hydrogen bonds. The conversion efficiency of L-amino acids to Damino acids by the uryl-based receptors is higher than that of the guanidinium-based ones.
Lijun Tang,Raju Nandhakumar,Gongfan Wei,Zhilong Guo 대한화학회 2011 Bulletin of the Korean Chemical Society Vol.32 No.9
An easy and convenient synthetic route to (S)-2-hydroxy-2'-(3-phenyluryl-benzyl)-1,1'-binaphthyl-3-carboxaldehyde (1), capable of recognizing tryptophan by fluorescence has been developed. The binol carboxaldehyde 1 exhibited a high selectivity to L-tryptophan over other examined L-α-amino acids such as alanine,phenylalanine, glutamine, arginine, lysine, serine, threonine, aspartat, valine, histidine and cysteine, with a fluorescence “turn-on” signal. In addition, 1 displayed chiral discrimination with good enantioselectivity toward L-tryptophan over D-tryptophan through different fluorescence enhancement factors.
Huang, Haofei,Nandhakumar, Raju,Choi, Misun,Su, Zhishan,Kim, Kwan Mook American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.7
<P>The chiral ketone (<I>S</I>)-<B>3</B> shows high kinetic enantioselectivities toward the <SMALL>l</SMALL> form for general underivatized amino acids with hydrophobic side chains and a high thermodynamic enantioselectivity toward the <SMALL>d</SMALL> form for cysteine with its −SH polar side chain when used as an extractant in enantioselective liquid–liquid extractions in the presence of Aliquat 336. Consecutive extractions by imine formation and hydrolysis increase the enantiopurity of the amino acid, as both of these reactions are <SMALL>l</SMALL>-form-selective.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-7/ja3105945/production/images/medium/ja-2012-105945_0011.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja3105945'>ACS Electronic Supporting Info</A></P>
The Chirality Conversion Reagent for Amino Acids Based on Salicyl Aldehyde
윤호진,Hein Jung,안윤수,Raju Nandhakumar,김준수,김관묵 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.5
2-Hydroxy-6-(1-(3-phenylurylphenyl)ethoxy)-benzaldehyde (2) has been synthesized in racemic form from 1,3-Dihydroxybenzene via formylation and reaction with 3-phenyluryl-methylbenzylbromide. The optically pure form of 2 was separated by normal silica column chromatography from the imine diastreomer which was obtained by the reaction of racemic mixture of 2 with optically pure leucinol. The absolute configuration of the separated enantiomer of 2 was decided from the energy calculation of the corresponding imine diastereomers. The activity of 2 as a chirality conversion reagent (CCR) for amino acids was determined by 1H NMR analysis. The efficiency of 2 is not better than the previous CCRs based on binaththol. Compound 2, however, has lower molecular weight compared to other CCRs. This work demonstrates that asymmetric carbon can control the selectivity of amino acids.